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This article is presented by:
Karan modgil
BACHELOR OF TECHNOLOGY In ELECTRICAL & ELECTRONICS ENGINEERING
2007 to 2011
ELECTRIC TRACTION SYSTEM
INTRODUCTION
A railway electrification system supplies electrical energy to railway locomotives and multiple units so that they can operate without having an on-board prime mover. There are several different electrification systems in use throughout the world. Railway electrification has many advantages but requires heavy capital expenditure for installation.
In India 1500 V DC and 25 kV AC, 50 Hz, is used for main line trains.
The 1500 V DC overhead system (negative earth, positive catenary) is used around Mumbai. The Mumbai region is the last bastion of 1500 V DC electrified lines on Indian Railways. There are plans to change this to 25 kV AC by 2010. The 25 kV AC system with overhead lines is used throughout the rest of the country. The dual-voltage WCAM series locomotives haul intercity trains out of Mumbai DC suburban region. The new AC/DC EMU rakes used in Mumbai are also designed to operate with both DC and AC traction as the Mumbai area switches over to the 25 kV AC system.
The Kolkata Metro uses 750 V DC traction with a third rail for delivering the electricity to the EMUs. The Kolkata trams use 550 V DC with overhead lines with underground conductors. The catenary is at a negative potential.
The Delhi Metro uses 25 kV AC overhead lines on the ground-level and elevated routes, and uses a rather unusual "rigid catenary", or overhead power rail, in the underground tunnel sections
The world's first AC locomotive in Valtellina (1898–1902). Power supply: 3-phase 15 Hz AC, 3000 V, (AC motor 70 km/h). It was designed by Kálmán Kandó in Ganz Company, Hungary.
Types of traction systems
Electric-traction systems can be broadly divided into those using alternating current and those using direct current. With direct current, the most popular line voltages for overhead wire supply systems have been 1,500 and 3,000. Third-rail systems are predominantly in the 600–750 volt range. The disadvantages of direct current are that expensive substations are required at frequent intervals and the overhead wire or third rail must be relatively large and heavy. The low-voltage, series-wound, direct-current motor is well suited to railroad traction, being simple to construct and easy to control. Until the late 20th century it was universally employed in electric and diesel-electric traction units.
The potential advantages of using alternating instead of direct current prompted early experiments and applications of this system. With alternating current, especially with relatively high overhead-wire voltages (10,000 volts or above), fewer substations are required, and the lighter overhead current supply wire that can be used correspondingly reduces the weight of structures needed to support it, to the further benefit of capital costs of electrification. In the early decades of high-voltage alternating current electrification, available alternating-current motors were not suitable for operation with alternating current of the standard commercial or industrial frequencies (50 hertz [cycles per second] in Europe; 60 hertz in the United States and parts of Japan). It was necessary to use a lower frequency (16 2/3 hertz is common in Europe; 25 hertz in the United States); this in turn required either special railroad power plants to generate alternating current at the required frequency or frequency-conversion equipment to change the available commercial frequency into the railroad frequency.
Characteristics of electric traction
The main advantage of electric traction is a higher power-to-weight ratio than forms of traction such as diesel or steam that generate power on board. Electricity enables faster acceleration and higher tractive effort on steep grades. On locomotives equipped with regenerative brakes, descending grades require very little use of air brakes as the locomotive's traction motors become generators sending current back into the supply system and/or on-board resistors, which convert the excess energy to heat.
Other advantages include the lack of exhaust fumes at point of use, less noise and lower maintenance requirements of the traction units. Given sufficient traffic density, electric trains produce less carbon emissions than diesel trains, especially in countries where electricity comes primarily from non-fossil sources.
The main disadvantage is the capital cost of the electrification equipment, most significantly for long distance lines which do not generate heavy traffic. Suburban railways with closely-spaced stations and high traffic density are the most likely to be electrified, and main lines carrying heavy and frequent traffic are also electrified in many countries.
• Current
o Direct current (DC)
o Alternating current (AC)
• Contact System
o third rail
o overhead line (catenary)
Overhead systems
Overhead lines
The Tyne and Wear Metro is the only United Kingdom system that uses 1,500 V DC.
1.5 kV DC is used in the Netherlands, Japan, Ireland, Australia (parts), India (around the Mumbai area alone[2], to be converted to 25 kV AC like the rest of the country[3]), France, New Zealand (Wellington) and the United States (Chicago area on the Metra Electric district and the South Shore Line interurban line). In Slovakia, there are two narrow-gauge lines in the High Tatras (one a cog railway). In Portugal, it is used in the Cascais Line, and in Denmark on the suburban S-train system.
loops at one end, causing the train to be reversed during every complete journey (intended to save having to run the locomotive round).
Advantages and disadvantages
Advantages include:
• lower running cost of locomotives and multiple units
• lower maintenance cost of locomotives and multiple units
• higher power-to-weight ratio, resulting in
o fewer locomotives
o faster acceleration
o higher practical limit of power
o higher limit of speed
• less noise pollution (quieter operation)
• reduced power loss at higher altitudes (for power loss see Diesel engine)
• lack of dependence on crude oil as fuel
